Recently, a pattern formed by the semiconductor process becomes more and more miniaturized, and whether a pattern is processed into a desired shape is inspected using a microscope. A microscope is a device that images a processed pattern and displays it on a display for measuring and inspecting the processed pattern using the image processing technology.
A microscope is classified roughly into two types, one is a microscope that detects a reflected light produced by focusing light (for example, laser beam) onto a sample and the other is a microscope that detects a secondary electron produced by focusing a charged particle beam (for example, an electron beam, an ion beam, etc.) onto a sample. An optical microscope and a microscope using a charged particle beam, though different in operation principle, can employ almost equivalent image processing technology. This is because both types of microscopes use the digital signal processing for producing images, though a high-resolution optical microscope detects a reflected light from a sample with the CCD sensor while a higher-resolution electron microscope detects electrons generated by a sample.
Because an optical microscope that has high resolution or a microscope that uses charged particles are used to measure or inspect extremely miniaturized objects, it is difficult for them to directly identify an object to be measured or inspected (hereinafter simply called an inspection object). Therefore, a method called template matching is used.
Template matching is a method for comparing multiple gradation values, which represent the unevenness of a pattern in a microscope image, with the template graphic image within a predetermined area for identifying a part with a high matching rate. Registering location information and a template in advance allows automatic measurement based on automatic location identification.
Patent Literature 1 describes a technology that enables a template to follow a change in the actual image based on a temporal change in the process condition or the device status by updating the template for each measurement.
Patent Literature 2 describes a technology that updates a template once for a predetermined number of measurements. In addition, Patent Literature 3 describes a method for changing a template, formed based on the design data, to a template based on a SEM (Scanning Electron Microscope) image.